Hello, I am adding a half bath and sub-dividing our bedroom to do so. I would rather not vent out the roof. I've studied what is available on this bulletin board and Studor's and Oatey's website (including Oatey's pdf's they offer) re: their air admittance valves. I am considering installing a Oatey Sure-Vent (not Sure-Vent II). The plan right now is to put the Sure-Vent about 6 inches above where the sink trap connects to the 1 1/2" T in the vanity cabinet itself, and to have the toilet downstream of the sink then both of them draining to the main drain which is ~7 feet away from the toilet drain. This would occur on the first floor of a two story house using what I think is called a gravity drain system (not pressurized). City plumbing. I wasn't planning on running any vents to the outside world. I may put some small holes in the vanity cabinet as an air intake for the valve. Has anyone done this and had any problems? Any advice? Thanks in advance! --Robert.